[PLUG] Re: [COS] gigabit ethernet

[Jeff McAdams <jeffm@iglou.com>]

Eric Hidle wrote:
> Speaking of fast networks, has anyone ever actually gotten gigabit ethernet
> stuff to do decent speed? I spent a ton of money on nice SMC switches that
> support jumbo frames and the SMC cards to go along with them, and I still
> can only get about 125mbit/s out of them. Slightly better than the 90 I got
> out of my 10/100 cards... but abyssmal for the cost... MTUs are 9K, but I
> still can't get any decent speed out of them... does anyone have experience
> in this?

Are they regular PCI cards?  33Mhz, 32-bit?  If so, then I'm not
surprised that you're not getting much more than 125mbit/s.  You could
probably get better with those cards, but you have to be careful about
how you spec everything out.

Keep in mind, first of all, that 33Mhz, 32-bit PCI only supports about
400mbit/s, and that's shared across the whole PCI bus.  Bumping up to
66Mhz and 64-bit PCI slots and card is an improvement (double the
throughput for each bump, there), and is enough to support gigabit
ethernet, if there's not a whole lot else going on in the system.  To
really get performance, you need to either have multiple PCI busses at
the higher speeds and width, or you need to go PCI-X, or both.

If you think about it...if you're pushing 125mbit/s in and out of your
gig card...that data has to go to or come from somewhere...most likely
your disk subsystem, or another NIC...so count on doubling that amount
of data on your PCI bus, at least...that get's you at 250mbit/s...plus
figure that your PCI bus is half-duplex, so if you're pushing data
through these cards at full duplex, you have to add that together...ok,
now you're getting into the range of saturating your PCI bus on your
machine.
-- 
Jeff McAdams
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor safety."
                                       -- Benjamin Franklin

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